1. Field of the Invention
The present invention relates to a semiconductor light-emitting device such as, for example, a semiconductor laser or a light emitting diode, and a method for fabricating the same. Alternatively, the present invention relates to a semiconductor laser usable as a light source in the fields of, for example, optical disks, laser beam printers and optical transmission, and especially relates to a semiconductor laser having an active layer of a multiple quantum well structure.
2. Description of the Related Art
As a conventional semiconductor laser, a quantum well type laser, including a quantum well layer as an active layer acting as a light emitting section, is known in the art. The quantum well type laser has various advantages including a lower operating current and improved noise characteristic. The quantum well type laser can have a separate confinement heterostructure (hereinafter, referred to as the xe2x80x9cSCH structurexe2x80x9d) for enhancing light confinement into the active layer.
In general, the forbidden band width a compound semiconductor layer and the refractive index thereof are in reverse proportion to each other. On the other hand, the Al mole fraction of a compound semiconductor layer containing Al and the forbidden band width thereof are typically in proportion to each other. Accordingly, the band diagram of the active layer and the vicinity thereof of a quantum well type laser having the SCH structure is, for example, as shown in FIG. 23.
A semiconductor laser having the band diagram shown in FIG. 23 includes a multiple quantum well (hereinafter, referred to as xe2x80x9cMQWxe2x80x9d) active layer 1501 which includes a plurality of quantum wells 1510 and a plurality of barrier layers 1511, and also includes a first optical guide layer 1502 and a second optical guide layer 1503 which interpose the active layer 1501 therebetween. Each of the first optical guide layer 1502 and the second optical guide layer 1503 has a larger forbidden band width than that of the quantum well layers 1510. The semiconductor laser further includes an n-type first cladding layer 1504 and a p-type second cladding layer 1505 which interpose the first and second optical guide layer 1502 and 1503 therebetween. Each of the n-type first cladding layer 1504 and the p-type second cladding layer 1505 have a larger forbidden band width than that of the first and second optical guide layers 1502 and 1503. In the semiconductor laser having such a structure, carrier confinement is established by the quantum well layers 1510, while light confinement is established by the first optical guide layer 1502 and the second optical guide layer 1503.
Such a semiconductor laser having the SCH structure is disclosed in, for example, Japanese Patent Publication for Opposition No. 4-67354 and Japanese Laid-Open Patent Publication No. 6-252508. The semiconductor laser disclosed in Japanese Patent Publication for Opposition No. 4-67354 contains impurities in the entire optical guide layers, while the semiconductor laser disclosed in Japanese Laid-Open Patent Publication No. 6-252508 contains no impurities in the optical guide layers.
The semiconductor laser disclosed in Japanese Patent Publication for Opposition No. 4-67354 includes an MQW active layer including a plurality of quantum well layers each having a thickness of no greater than the de Brogli wavelength of electrons, i.e., a thickness of about 20 nm or less. Referring to FIG. 24, such a semiconductor laser 1700 includes an n-type GaAs buffer layer 1702, an n-type AlGaAs cladding layer 1703, an n-type AlGaAs guide layer 1704, an MQW active layer 1705, a p-type AlGaAs guide layer 1706, a p-type AlGaAs cladding layer 1707, and a p-type GaAs cap layer 1708, which are formed on an n-type GaAs substrate 1701 in the above order.
FIG. 25 is an energy band diagram of the MQW active layer 1705 and the vicinity thereof. As shown in FIG. 25, the MQW active layer 1705 includes a plurality of GaAs quantum well layers 1710 and a plurality of AlGaAs quantum barrier layers 1711 each interposed between two adjacent quantum well layers 1710. In the example shown in FIG. 25, the MQW active layer 1705 includes three GaAs quantum well layers 1710 and two AlGaAs quantum barrier layers 1711 provided alternately.
The forbidden band width of each of the n-type AlGaAs guide layer 1704 and the p-type AlGaAs guide layer 1706 is set to be equal to the forbidden band width of the quantum barrier layers 1711. By setting the forbidden band widths of the AlGaAs guide layers 1704 and 1706 and the quantum barrier layers 1711 at the same value, the quantum well layers 1710 are all interposed between two semiconductor layers having the same width forbidden band width. Thus, the dispersion of the quantization level is reduced among the quantum well layers 1710, which leads to a narrower light emitting spectrum. Accordingly, the threshold current is lowered.
Recently, a further reduction in the threshold current of semiconductor lasers has been demanded. In order to further reduce the threshold current in the semiconductor laser 1700, the light confinement ratio into the quantum well layers 1710 of the MQW active layer 1705 is required to be raised. In the SCH structure, the light confinement ratio can be raised to reduce the threshold current by increasing the thickness of the optical guide layers 1704 and 1706. Accordingly, it is desirable to increase the thickness of the optical guide layers in order to reduce the threshold current.
However, thicker optical guide layers cause the following problems.
In general, a dopant concentration of the optical guide layer is set to be significantly lower than that of the cladding layer (alternatively, no doping is performed into the optical guide layer) in order to suppress the dopant diffusion from the optical guide layer to the MQW active layer. Accordingly, thicker optical guide layers increase the resistance of the semiconductor laser in the optical guide layer, resulting in an increased operating voltage. As can be appreciated, the thicker optical guide layer according to the conventional technology causes the device characteristics to be deteriorated due to an increased operating voltage, while a reduced threshold current can be realized thereby.
In the semiconductor laser 1700, the forbidden band width of the optical guide layers 1704 and 1706 is set to be equal to the forbidden band width of the quantum barrier layers 1711. Such setting corresponds to setting the Al mole fraction of the optical guide layers 1704 and 1706 to substantially as high as the Al mole fraction of the quantum barrier layer 1711. Accordingly, the dopant in the cladding layers 1703 and 1707 may be diffused to the MQW active layer 1705, whereby the Al mole fraction of the quantum well layers 1710 is likely to change. As a result, the oscillating wavelength is shifted from the designed value, resulting in difficulty in controlling the oscillating wavelength.
In the case of the semiconductor laser disclosed in Japanese Laid-Open Patent Publication No. 6-252508 which does not contain impurities in the optical guide layer, the thicker optical guide layer causes an increased resistance thereof. In addition, there occurs a potential barrier between the cladding layer and the optical guide layer, thereby raising the operating voltage.
In the case of the semiconductor laser 1700 disclosed in Japanese Patent Publication for Opposition No. 4-67354 containing impurities in the optical guide layers 1704 and 1706, the impurities are diffused from the optical guide layers 1704 and 1706 to the MQW active layer 1705 during activation of the semiconductor laser 1700. Accordingly, a non-emission recombination center is formed in the MQW active layer 1705, resulting in an inner absorption loss. Thus, characteristics of the semiconductor laser 1700 are deteriorated.
Moreover, the details of influences on the laser characteristics caused by impurity injection into semiconductor layers, such as optical guide layers, which are adjacent to the active layer have not received much study.
The above-described problems are also applied to semiconductor lasers other than those of the quantum well type, and also to light emitting diodes including cladding layers interposing an active layer.
A light-emitting device of the present invention includes: a first guide layer; a second guide layer; and an active layer interposed between the first guide layer and the second guide layer. The active layer having a multiple quantum well structure including a plurality of quantum well layers and a quantum barrier layer interposed between the adjacent quantum well layers. The first guide layer and the second guide layer are disposed to be adjacent to the quantum well layers. The first guide layer and the second guide layer have a forbidden band width which is larger than a forbidden band width of the quantum well layers. The forbidden band width of at least one of the first guide layer and the second guide layer is smaller than a forbidden band width of the quantum barrier layer.
In one embodiment, the device further includes: a first cladding layer having a first conductivity type and a second cladding layer having a second conductivity type, the first cladding layer and the second cladding layer interposing the first guide layer and the second guide layer; and a saturable absorption layer provided between the first cladding layer and the second cladding layer, the saturable absorption layer having a light emitting energy of a level substantially equal to an energy of a laser oscillation light of the active layer.
In another embodiment, the device further includes: a first cladding layer having a first conductivity type and a second cladding layer having a second conductivity type, the first cladding layer and the second cladding layer interposing the first guide layer and the second guide layer; a third cladding layer having the second conductivity type and provided outside the second cladding layer, the third cladding layer being disposed on the opposite side to the first cladding layer with respect to the second cladding layer; and a saturable absorption layer provided between the first cladding layer and the third cladding layer, the saturable absorption layer having a light emitting energy of a level substantially equal to an energy of a laser oscillation light of the active layer.
In still another embodiment, the device further includes: a first cladding layer having a first conductivity type and a second cladding layer having a second conductivity type, the first cladding layer and the second cladding layer interposing the first guide layer and the second guide layer; and a striped third cladding layer having the second conductivity type and provided outside the second cladding layer, the striped third cladding layer being disposed on the opposite side to the first cladding layer with respect to the second cladding layer, wherein a difference xcex94n between a refractive index na of light confined in a first portion of the active layer which is covered by the striped third cladding layer and a refractive index nb of light confined in a second portion of the active layer which is not covered by the striped third cladding layer fulfills expression (1).
xe2x80x832xc3x9710xe2x88x923xcex94nxe2x89xa67xc3x9710xe2x88x923xe2x80x83xe2x80x83(1).
The second cladding layer having the second conductivity type may be a p-type cladding layer, the second guide layer may be disposed on the same side as the p-type cladding layer with respect to the active layer, and the forbidden band width of the second guide layer may be smaller than the forbidden band width of the quantum barrier layer.
The smaller one of the forbidden band width of the first guide layer and that of the second guide layer may be larger than a forbidden band width value corresponding to an energy of a laser oscillation light of the active layer.
Eg, Eb and Excex may fulfill expression (2) where Eg is the smaller one of the forbidden band width of the first guide layer and that of the second guide layer, Eb is the forbidden band width of the quantum barrier layer, and Excex is the forbidden band width value corresponding to the energy of the laser oscillation light energy of the active layer: Excex+100 meVxe2x89xa6Egxe2x89xa6Ebxe2x88x9250 meV . . . (2).
Another light-emitting device of the present invention includes a layered structure including at least an active layer, wherein at least one selected layer in the layered structure includes an impurity-scarce region and an impurity-doped region, and the impurity-scarce region is disposed closer to the active layer than the impurity-doped region.
In one embodiment, the layered structure includes a pair of cladding layers interposing the active layer, and the at least one selected layer is at least one of the pair of cladding layers.
In another embodiment, the layered structure includes a pair of optical guide layers interposing the active layer, and the at least one selected layer is at least one of the pair of optical guide layers.
In still another embodiment, the layered structure includes an optical guide layer disposed on either side of the active layer, and the at least one selected layer is the optical guide layer.
The device may further include an intermediate impurity concentration region between the impurity-scarce region and the impurity-doped region.
The active layer may include a quantum well layer.
In one embodiment, the at least one selected layer is an optical guide layer, and the impurity-doped region may contain a p-type impurity at a carrier concentration of 4xc3x971017 cmxe2x88x923 or more and 1.2xc3x971018 cmxe2x88x923 or less.
In another embodiment, the at least one selected layer is an optical guide layer, and the impurity-doped region contains an n-type impurity at a carrier concentration of 2xc3x971017 cmxe2x88x923 or more and 1xc3x971018 cmxe2x88x923 or less.
An impurity concentration of the impurity-scarce region may be ⅕ or less of an impurity concentration of the impurity-doped region.
The impurity-scarce region may have a thickness of 3 nm or more and 10 nm or less.
The impurity-scarce region may be provided in at least one of a p-type cladding layer and a p-type optical guide layer.
In one embodiment, the layered structure includes a p-type cladding layer and an n-type cladding layer interposing the active layer, the impurity-scarce region is provided in each of the p-type cladding layer and the n-type cladding layer, and the impurity-scarce region in the p-type cladding layer is thicker than the impurity-scarce region in the n-type cladding layer.
In another embodiment, the layered structure includes a p-type optical guide layer and an n-type optical guide layer interposing the active layer, the impurity-scarce region is provided in each of the p-type optical guide layer and the n-type optical guide layer, and the impurity-scarce region in the p-type optical guide layer is thicker than the impurity-scarce region in the n-type optical guide layer.
The intermediate impurity concentration region may have a thickness of 3 nm or more and 10 nm or less.
In one embodiment, the active layer has a multiple quantum well structure including a plurality of quantum well layers and a barrier layer interposed by the adjacent quantum well layers, and a forbidden band width of at least the impurity-doped region of the at least one selected layer is smaller than a forbidden band width of the barrier layer and larger than a forbidden band width of the quantum well layers.
The forbidden band width of the impurity-doped region may be smaller than the forbidden band width of the impurity-scarce region.
The at least one selected layer may be formed of a material selected from the group consisting of AlGaAs type materials, AlGaInP type materials and InGaN type materials.
Another aspect of the present invention provides a method for fabricating a light-emitting device which includes a layered structure including at least an active layer, wherein at least one selected layer in the layered structure includes an impurity-scarce region, an impurity-doped region, and an intermediate impurity concentration region disposed between the impurity-scarce region and the impurity-doped region, the impurity-scarce region being disposed closer to the active layer than the impurity-doped region. The method includes the steps of: growing an impurity-doped layer and a non-impurity-doped layer; and diffusing an impurity from the impurity-doped layer to the non-impurity-doped layer by thermal hysteresis during crystal growth, thereby forming the intermediate impurity concentration region.
In one embodiment, the layered structure is formed so as to include a p-type cladding layer and an n-type cladding layer interposing the active layer, the impurity-scarce region is provided in each of the p-type cladding layer and the n-type cladding layer, and the impurity-scarce region in the p-type cladding layer is formed to be thicker than the impurity-scarce region in the n-type cladding layer.
In another embodiment, the layered structure is formed to include a p-type optical guide layer and an n-type optical guide layer interposing the active layer, the impurity-scarce region is provided in each of the p-type optical guide layer and the n-type optical guide layer, and the impurity-scarce region in the p-type optical guide layer is formed to be thicker than the impurity-scarce region in the n-type optical guide layer.
In the above-described structure, setting the forbidden band width of the guide layers to be smaller than the forbidden band width of the quantum barrier layer corresponds to setting the refractive index of the guide layers to be larger than the refractive index of the quantum barrier layer. Accordingly, the above setting provides an enhanced light confinement ratio in the quantum well layers in the multiple quantum well (or MQW) active layer, thereby reducing the threshold current. Furthermore, it is not necessary to increase the thickness of the guide layers as is necessary in the conventional examples for the purpose of reducing the threshold current, and thus the operating voltage is prevented from being increased which would otherwise be caused by the increased device resistance in the conventional art.
In the case where the semiconductor device is formed of, for example, Al-type semiconductor materials, setting the forbidden band width of the guide layers to be smaller than the forbidden band width of the quantum barrier layer corresponds to setting the Al mole fraction of the guide layers to be lower than the Al mole fraction of the quantum barrier layer. Accordingly, dopant diffusion from the cladding layers to the guide layers is suppressed by the above setting. Since the dopant diffusion to the MQW active layer is also suppressed, the Al mole fraction of the quantum well layers in the MQW active layer is restricted from changing, thereby preventing the oscillation wavelength from shifting.
Controlling the forbidden band width of the guide layers corresponds to controlling the refractive index thereof. Accordingly, the vertical radiation angle is allowed to be adjusted by appropriately setting the refractive indices of the two guide layers.
When the Al mole fraction of the guide layers is set to be lower than the Al mole fraction of the quantum barrier layer, the number of the non-emission recombination levels in the guide layers is reduced. Accordingly, non-emission recombination is restricted with respect to carriers leaking to the guide layers from the quantum well layers. Thus, the carriers are used effectively for light emission so as to reduce the threshold current.
In the case where a saturable absorption layer with a forbidden band width having a light emitting energy level which is substantially equal to an energy level of the laser oscillation light of the MQW active layer is provided between two cladding layer, for example, between the first and second cladding layers or between the first and third cladding layers, self-sustaining pulsation occurs; i.e., laser light oscillates in the form of pulses. In the self-sustaining pulsation condition, the longitudinal lasing mode becomes a multiple mode, and thus the spectral line width of each of the longitudinal modes is enlarged. Therefore, coherency of the laser is reduced and is not influenced by the returning light, resulting in reduced noise.
In the structure having the saturable absorption layer, dopant diffusion from the cladding layer provided between the MQW active layer and the saturable absorption layer is suppressed by the saturable absorption layer. In consequence, it is considered that dopant diffusion to the MQW active layer may undesirably increase. However, since the Al mole fraction of the guide layers is set to be smaller than the Al mole fraction of the quantum barrier layer, the dopant diffusion from the cladding layers to the guide layers is suppressed. Accordingly, the dopant diffusion to the MQW active layer is suppressed. Thus, the Al mole fraction of the quantum well layers of the MQW active layer is prevented from changing and, consequently, the oscillation wavelength is prevented from shifting.
In the case where the striped third cladding layer is provided and the refractive index difference xcex94n is set within the range of expression (1), the amount of saturable absorption increases in a portion of the active layer which is not covered by the striped third cladding layer. Thus, self-sustaining pulsation occurs while the light is confined in a portion of the active layer which is covered by the striped third cladding layer. In consequence, there exists less influence due to wave fronts caused by the saturable absorption effect in the portion of the active layer which is not covered by the striped third cladding layer. Therefore, a beam spot of the emitted light is less shifted in a horizontal direction, thereby reducing the astigmatic difference and improving the optical characteristics of the semiconductor laser.
The degree of dopant diffusion depends on constituting materials of the cladding layers. For example, in the case of AlGaInP-type cladding layers, the dopant in a p-type cladding layer is more likely to diffuse as compared to the case of AlGaAs-type cladding layers. According to the present invention, even in such a case, the wavelength is prevented from shifting more effectively by setting the forbidden band width of the second guide layer, provided on the side of the p-type cladding layer, to be smaller than that of the quantum barrier layers so as to restrict the dopant diffusion to the active layer.
In the case where the forbidden band width of either one of the two guide layers which is smaller is set to be larger than a forbidden band width level corresponding to the laser oscillation light energy of the active layer, the threshold current is reduced more effectively.
Especially in the case where the smaller forbidden band width Eg of the two guide layers is set to fulfill expression (2), the threshold current is reduced more effectively.
Moreover, according to the present invention, at least one of the cladding layers interposing the active layer may include an impurity-scarce region and an impurity-doped region. The impurity-scarce region, having a lower impurity concentration than that of the impurity-doped region, is disposed closer to the active layer. Accordingly, impurity diffusion from the impurity-doped region to the active layer during the operation is blocked at the impurity-scarce region.
Alternatively, in the case where at least one of the optical guide layers interposing the active layer includes an impurity-doped region, the resistance of the entire optical guide layers is lowered. Furthermore, the diffusion potential between the optical guide layer and the cladding layer is lowered, and thus, the operating voltage is reduced. In addition, since the impurity-scarce region, having a lower impurity concentration than that of the impurity-doped region, is disposed closer to the active layer, impurity diffusion from the impurity-doped region to the active layer during the operation is blocked at the impurity-scarce region. Thus, the reliability of the device is improved.
In the case where the optical guide layer provided on one side of the active layer includes an impurity-doped region, the resistance of the entire optical guide layers is lowered. Furthermore, the diffusion potential between the optical guide layer and the cladding layers is lowered, the operating voltage is reduced. In addition, since the impurity-scarce region, having a lower impurity concentration than that of the impurity-doped region, is disposed closer to the active layer, impurity diffusion from the impurity-doped region to the active layer during the operation is blocked at the impurity-scarce region. Thus, the reliability of the device is improved.
In the case where the intermediate impurity concentration region having an impurity concentration which is lower than that of the impurity-doped region but higher than that of the impurity-scarce region is provided between the impurity-scarce region and the impurity-doped region, impurity diffusion from the impurity-doped region to the impurity-scarce region during the operation is blocked. Thus, the reliability of the device is further improved.
Especially, when the active layer includes a quantum well layer, even a slight impurity diffusion is generally likely to cause changes in the layered structure resulting in the deteriorated device characteristics. However, the present invention is very effective for restricting impurity diffusion to the active layer during the operation even in such a case.
In the case where the impurity in the impurity-doped region of the optical guide layer is of the p-type, the carrier concentration of the impurities is preferably set to 4xc3x971017 cmxe2x88x923 or more and 1.2xc3x971018 cmxe2x88x923 or less. In the case where the impurity in the impurity-doped region of the optical guide layer-is of the n-type, the carrier concentration of the impurities is preferably set to 2xc3x971017 cmxe2x88x923 or more and 1xc3x971018 cmxe2x88x923 or less. Due to such setting, the operation voltage is effectively reduced, and deterioration of the device characteristics otherwise caused by non-emission recombination of the carriers in the impurity-doped region is effectively suppressed. Regarding the impurity concentration in the impurity-doped region of the cladding layers, any concentration at which the carrier confinement into the active layer is realized is appropriate.
The carrier concentration of the impurities in the impurity-scarce region is preferably set to ⅕ or less of that in the impurity-doped region in order to effectively suppress impurity diffusion to the active layer during the operation.
The thickness of the impurity-scarce region is preferably set to be 3 nm or more and 10 nm or less. When the thickness is less than 3 nm, the impurity diffusion into the active layer during the operation occurs, which is likely deteriorate the device characteristics. When the thickness is more than 10 nm, carrier injection from the impurity-doped region to the active layer is inhibited by the potential barrier, which is likely to raise the operating voltage. Regarding the thickness of the impurity-doped region of the cladding layers, any thickness at which the carrier confinement into the active layer is realized is appropriate. Regarding the thickness of the impurity-doped region of the optical guide layer, any thickness at which the light confinement into the active layer is realized is appropriate.
The impurity-scarce region can be provided in only a p-type cladding layer or a p-type optical guide layer, since a p-type impurity, which has a larger diffusion coefficient than an n-type impurity, is more likely to diffuse to the active layer and thus is more likely to deteriorate the device characteristics. In such a structure, the device designing is relatively easily performed since only the thickness control of the p-type impurity-scarce region is required.
The impurity-scarce region provided in the p-type cladding layer or the p-type optical guide layer can be thicker than the impurity-scarce region provided in the n-type cladding layer or the n-type optical guide layer. In such a structure, the thickness of the impurity-scarce region can be controlled in accordance with the degree of diffusion of the p-type impurity having a larger diffusion coefficient than that of the n-type impurity. Accordingly, the device can be designed with higher controllability.
The thickness of the intermediate impurity concentration region is preferably set to be 3 nm or more and 10 nm or less. A thickness within this range effectively prevents impurity diffusion from the impurity-doped region to the impurity-scarce region during the operation without inhibiting carrier injection from the impurity-doped region to the active layer.
When the active layer includes a multiple quantum well layer, the forbidden band width of at least the impurity-doped region of the optical guide layer can be smaller than the forbidden band width of the quantum barrier layer but larger than the forbidden band width of the quantum well layers. In general, in a compound semiconductor material containing Al, the Al mole fraction is in proportion to the forbidden band width, and the Al mole fraction can be lowered by reducing the forbidden band width of the impurity-doped region. Thus, the impurity diffusion from the impurity-doped region to the active layer is further reduced. This allows a thinner impurity-scarce region, which is effective in reducing the operating voltage.
The forbidden band width of the entire optical guide layer including the impurity-scarce region and the intermediate impurity concentration region can be smaller than the forbidden band width of the barrier layer but larger than the forbidden band width of the quantum well layers. When the forbidden band width of the impurity-doped region is smaller than the forbidden band width of the impurity-scarce region, the carrier confinement into the active layer is established by the impurity-scarce region. Accordingly, the Al mole fraction of the impurity-doped region can be further lowered so as to further reduce impurity diffusion from the impurity-doped region to the active layer. This allows a thinner impurity-scarce region, which is effective in reducing the operating voltage.
The cladding layers and/or the optical guide layers can be formed of, for example, AlGaAs-type materials, AlGaInP-type materials, or InGaN-type materials. The present invention is especially effective for the AlGaInP-type materials, since impurities are more likely to diffuse in this type of materials, as compared to the AlGaAs-type materials. The present invention is also effective for the InGaN-type materials, which have a higher growth temperature and are more likely to cause impurity diffusion, as compared to the AlGaInP-type materials.
According to the present invention, the intermediate impurity concentration region can be formed by diffusing impurities from the impurity-doped layer to the non-impurity-doped layer by thermal hysteresis during the crystal growth. Thus, the impurity-doped region, the intermediate impurity concentration region, and the impurity-scarce region can be formed through a simple fabrication process with satisfactory controllability. This thermal hysteresis temperature (i.e., the crystal growth temperature) is typically set, for example, at 600xc2x0 C. to 800xc2x0 C. in the case of the AlGaAs-type materials, 500xc2x0 C. to 700xc2x0 C. in the case of the AlGaInP-type materials, and 900xc2x0 C. to 1100xc2x0 C. in the case of the InGaN-type materials. The intermediate impurity concentration region can be formed at a temperature lower than the growth temperature of the active layer by about 50xc2x0 C. to 200xc2x0 C. in order to control the impurity diffusion.
The non-impurity-doped region provided in the p-type cladding layer or the p-type optical guide layer can be thicker than the non-impurity-doped region provided in the n-type cladding layer or the n-type optical guide layer. In such a structure, the thickness of the impurity-scarce region can be controlled by controlling the thickness of the non-impurity-doped regions in accordance with the degree of diffusion of the p-type impurity having a larger diffusion coefficient than that of the n-type impurity. Accordingly, the device can be designed with higher controllability.
Thus, the invention described herein makes possible the advantages of providing: (1) a light-emitting device capable of reducing the operating voltage while maintaining satisfactory characteristics, and a method for fabricating the same; (2) a light-emitting device capable of reducing the threshold current without increasing the operating voltage, and a method for fabricating the same; and (3) a light-emitting device capable of preventing the oscillating wavelength from being shifted, and a method for fabricating the same.